Alkoxylated sucrose esters are useful as surfactants, lubricants, emulsifiers, and cleaning agents. By varying the degree of esterification, the properties of the alkoxylated sucrose esters can range from those useful for emulsifiers, aqueous-based surfactants, etc. (generally lower esterification) to those useful for oil-soluble surfactants, cleaning agents, etc. (generally higher esterification).
Several methods are known for producing sucrose esters with varying degrees of esterification. For instance, Rizzi and Taylor, U.S. Pat. No. 3,963,699, describe a solvent-free transesterification process in which a mixture of a polyol (such as sucrose), a fatty acid lower alkyl ester (such as a fatty acid methyl ester), an alkali metal fatty acid soap, and a basic catalyst is heated to form a homogenous melt, to which is added excess fatty acid lower alkyl ester to form the higher polyol fatty acid polyesters.
Feuge et al, U.S. Pat. No. 3,714,144, and Feuge et al, J. Amer. Oil Chem. Soc., 1970, 47(2), 56-60, disclose a solvent-free transesterification process which includes mixing molten sucrose with esters of fatty acids and alkali-free sodium or potassium soaps under a partial vacuum. The teachings of Feuge et al are generally directed to the formation of lower esters; the only specific teaching by Feuge et al of a method in which the percentage of sucrose esters having three or more fatty acid chains is greater than 35% of the total sucrose esters formed uses methyl carbitol palmitate as a fatty acid source.
Osipow et al, U.S. Pat. No. 4,380,616, disclose the preparation of sucrose mono- and di-esters by forming a transparent emulsion containing immiscible reactants and maintaining the transparent emulsions under appropriate conditions to permit reaction. Sucrose mono- and di-esters are formed using emulsions containing methyl fatty acid ester and sucrose. Osipow et al also disclose the formation of mono- and di-glycerides using emulsions containing glycerine and methyl fatty acid esters or glycerol tri-esters.
Also known are various methods for producing alkoxylated sucrose esters. Ennis et al, U.S. Pat. No. 5,077,073, disclose a process for preparing alkoxylated sucrose esters made from alkoxylated sucrose that is reacted in a solvent to form the alkoxylated sucrose esters. This material then may be used as a fat substitute. Ferenz, U.S. Pat. No. 5,427,815, discloses the process for preparing linked, alkoxylated, esterified polyols made from alkoxylated polyols that are then esterified with a polycarboxylate segment. Handwerker et al, U.S. Pat. No. 5,362,894 and Cooper et al, U.S. Pat. No. 5,512,313, disclose similar processes for preparing alkoxylated esterified polyols made from alkoxylated polyols that are then esterified. Porta et al, U.S. Pat. No. 6,486,120, disclose the use of alkoxylated sucrose esters in liquid, aqueous softening compositions. Again, the methodology disclosed involves first alkoxylating the sucrose in a solvent and then esterifying to form the alkoxylated sucrose esters.
Cooper, U.S. Pat. No. 5,118,448, discloses a process for preparing alkoxylated esterified polyols that involves first reacting a benzylated polyol with an epoxide. The process to form the benzylated polyol raw material involves a reaction between a polyol and an aldehyde or ketone to form an acetal or ketal. The acetal or ketal is then reacted with alkali metal and benzyl halide to give the mono-benzyl ether of the acetal or ketal. This mono-benzyl ether is then hydrolyzed in the presence of dilute acid to give the benzylated polyol. The benzylated polyol is then reacted with epoxide to form an alkoxylated, benzylated polyol. The resulting mixture is then reacted with hydrogen to convert the benzyl group to a hydroxyl group. The hydroxyl group is then esterified using a fatty acid compound such as a fatty acid, fatty acid ester, or fatty acid halide. Like the processes previously described, this process involves alkoxylating prior to esterifying, though it claims to produce a material with at least one ester group directly bonded to the polyol backbone.
Generally, these known processes for making alkoxylated sucrose esters suffer from the requirement of using a solvent to first alkoxylate the sucrose. In the case of Cooper, U.S. Pat. No. 5,118,448, a solvent would be required to first benzylate the sucrose, as this step precedes the alkoxylation step. The use of a solvent to dissolve sucrose results in solvent present as an impurity in the final product and/or undesirable side reactions between the solvent and other elements which produce unwanted reaction products.
For instance, Cooper, U.S. Pat. No. 5,118,448, discloses a process for producing a material with at least one ester group bonded directly to the polyol backbone. However, this process will also undoubtedly produce unwanted by-products. These by-products may be produced in one or more of several ways. First, they may be formed during the formation of the benzylated polyol from the starting polyol, which typically involves reacting the polyol with either an aldehyde or a ketone to form an acetal or a ketal. These acetals or ketals are then reacted with alkali metal and benzyl halide to produce the mono-benzyl ether of the acetal or ketal. The mono-benzyl ether is then reacted with dilute acid and water to form the benzylated polyol. Secondly, by-products may be formed when the benzylated, alkoxylated polyol is then reacted with hydrogen in the presence of a transition metal hydrogenalysis catalyst to form the alkoxylated polyol. These by-products may include unremoved aldehydes, ketones, acetals, ketals, mono-benzyl ethers, and benzyl halide.
By-products such as these are problematic because they affect the functionality of the individual alkoxylated sucrose ester and may have a negative impact on the purity of a finished product that incorporates such alkoxylated sucrose esters. Furthermore, should these alkoxylated sucrose esters be approved for use in food products, such by-products will in all likelihood be banned from inclusion in such food products.
Accordingly, there is a need for alkoxylated sucrose esters having reduced levels of by-products and processes for producing such improved alkoxylated sucrose esters.